Analytical solutions for the normal stress differences in large-amplitude oscillatory shear flow (LAOS), for continuum or molecular models, normally take the inexact form of the first few terms of a series expansion in the shear rate amplitude. Here, we improve the accuracy of these truncated expansions by replacing them with rational functions called Padé approximants. The recent advent of exact solutions in LAOS presents an opportunity to identify accurate and useful Padé approximants. For this identification, we replace the truncated expansion for the corotational Jeffreys fluid with its Padé approximants for the normal stress differences. We uncover the most accurate and useful approximant, the [3,4] approximant, and then test its accuracy against the exact solution [C. Saengow and A. J. Giacomin, “Normal stress differences from Oldroyd 8-constant framework: Exact analytical solution for large-amplitude oscillatory shear flow,” Phys. Fluids 29, 121601 (2017)]. We use Ewoldt grids to show the stunning accuracy of our [3,4] approximant in LAOS. We quantify this accuracy with an objective function and then map it onto the Pipkin space. Our two applications illustrate how to use our new approximant reliably. For this, we use the Spriggs relations to generalize our best approximant to multimode, and then, we compare with measurements on molten high-density polyethylene and on dissolved polyisobutylene in isobutylene oligomer.
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April 2018
Research Article|
March 26 2018
Padé approximant for normal stress differences in large-amplitude oscillatory shear flow
Special Collection:
Papers Selected from the Seventh International Symposium on Physics of Fluids
P. Poungthong
;
P. Poungthong
1
Polymer Research Center, Mechanical and Aerospace Engineering Department, King Mongkut’s University of Technology North Bangkok
, Bangkok 10800, Thailand
2
Polymers Research Group, Chemical Engineering Department, Queen’s University
, Kingston, Ontario K7L 3N6, Canada
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C. Saengow
;
C. Saengow
2
Polymers Research Group, Chemical Engineering Department, Queen’s University
, Kingston, Ontario K7L 3N6, Canada
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A. J. Giacomin
;
A. J. Giacomin
a)
2
Polymers Research Group, Chemical Engineering Department, Queen’s University
, Kingston, Ontario K7L 3N6, Canada
3
Mechanical and Materials Engineering Department, Queen’s University
, Kingston, Ontario K7L 3N6, Canada
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C. Kolitawong;
C. Kolitawong
1
Polymer Research Center, Mechanical and Aerospace Engineering Department, King Mongkut’s University of Technology North Bangkok
, Bangkok 10800, Thailand
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D. Merger;
D. Merger
4
Institut für Technische Chemie und Polymerchemie, Karlsruher Institut für Technologie
, 76128 Karlsruhe, Germany
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M. Wilhelm
M. Wilhelm
4
Institut für Technische Chemie und Polymerchemie, Karlsruher Institut für Technologie
, 76128 Karlsruhe, Germany
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a)
Author to whom correspondence should be addressed: giacomin@%20queensu.ca.
Physics of Fluids 30, 040910 (2018)
Article history
Received:
November 11 2017
Accepted:
December 09 2017
Citation
P. Poungthong, C. Saengow, A. J. Giacomin, C. Kolitawong, D. Merger, M. Wilhelm; Padé approximant for normal stress differences in large-amplitude oscillatory shear flow. Physics of Fluids 1 April 2018; 30 (4): 040910. https://doi.org/10.1063/1.5013203
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